Thermal and X‐ray powder diffraction studies of aliphatic polyester dendrimers

The syntheses and thermal and X‐ray powder diffraction analyses of three sets of aliphatic polyester dendrimers based on 2,2‐bis(hydroxymethyl)propionic acid as a repeating unit and 2,2‐dimethyl‐1,3‐propanediol, 1,5‐pentanediol, and 1,1,1‐tris(hydroxymethyl)ethane as core molecules are reported. These dendritic polyesters were prepared in high yields with the divergent method. The thermal properties of these biodendrimers were evaluated with thermogravimetric analysis and differential scanning calorimetry. The thermal decomposition of the compounds occurred around 250 °C for the hydroxyl‐ended dendrimers and around 150 °C for the acetonide‐protected dendrimers. In addition, the crystallinity of the lower generation dendrimers was evaluated with X‐ray powder diffraction. The highest crystallinity and the highest melting points were observed for the first‐generation dendritic compounds. The higher generation dendrimers showed weaker melting transitions during the first heating scan. Only the glass‐transition temperatures were observed in subsequent heating scans. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5574–5586, 2004     

Evaluation of DNA Binding with Some Selected Hydrazide and Semicarbazide Derivatives

A group of hydrazide and semicarbazide derivatives containing isopropylidene, benzylidene, cyclohexylidene, and phospholidene groups was synthesized and characterized by spectroscopic techniques. These compounds were tested for DNA interaction studies monitored by UV-Vis and IR data as well as molecular docking. Investigations on interactions of these compounds with DNA revealed an intercalative mode of binding between them. It is interesting to note that semicarbazide derivatives with aliphatic substituents showed better DNA binding than the aromatic substituents.     

Synthesis and Structure of Trimethylplatinum(IV) Iodide Complex of 4'-(4-Methoxyphenyl)-2,2':6',2'-terpyridine Ligand and its Halogen Bonding Property

The synthesis and structural characterization of a new trimethylplatinum(IV) iodide complex of 4'-(4-methoxyphenyl)-2,2':6',2''-terpyridine ligand L, {PtMe₃IL} ( 1 ) is reported. The X-ray crystal structure shows that the terpyridine ligand L binds the platinum(IV) metal center in bidentate fashion, which is well supported by the ¹H NMR spectrum of 1 . The complex 1 upon crystallization with 1,4-diiodotetrafluorobenzene (DITFB) forms the halogen bonded complex 1a ( 1· DITFB). The structural investigation shows that 1a exhibits the halogen bonding interaction in which the non-coordinated pyridyl nitrogen acts as halogen bond acceptors by forming I ··· N interaction with iodine atom of DITFB. In addition iodine atom of complex 1 also acts as weak halogen bond acceptor.     

Synthesis and biological evaluation of 4,5,6,7-tetrahydrothieno[2,3-c]pyridine–based β-aminonitriles and their derivatives: β-amino carboxamides, (thio)ureas,and tetracycles

The preparation and cytotoxic characterization of 4,5,6,7-tetrahydrothieno[2,3-c]pyridine–based β-aminonitriles, β-amino carboxamides, and their (thio)urea and annulated derivatives were accomplished. Following a synthetic route involving Gewald three-component reactions (G-3CR) and a Lewis acid–catalyzed iso (thio)cyanate coupling, 30 compounds were prepared for antitumor evaluation. For derivatizations, a catalytic amount of CuOAc₂ (20 mol%) was essential for improving the reactivity of either the C-2 amino function of thiophene or isocyanates. The synthesized analogues demonstrated a weak to moderate antitumor activity in a low micromolar range against A549 and K562 cancer cell lines.     

A New Structural Motif for an Enantiomerically Pure Metallosupramolecular Pd4L8 Aggregate by Anion Templating

An enantiomerically pure BINOL‐based bis(3‐pyridyl) ligand 1 assembles into a homochiral [Pd₄( 1 )₈] complex upon coordination to tetravalent Pd^II ions. The formation of this aggregate is templated by two tetrafluoroborate counterions that are encapsulated in two peripheral cavities. The resulting structure is a new structural motif for this kind of metallosupramolecular assemblies that arranges the palladium ions in a distorted tetrahedral fashion and forces ligand 1 to adopt two different conformations. Both phenomena are unique and cause an overall three‐dimensional structure that has another confined, chiral, and hydrophilic central cavity.     

Properties and Polymerization of Biodegradable Thermoplastic Poly(Ester-urethane)

Abstract

Aliphatic polyesters, such as poly(lactic acids), need high molecular weight for acceptable mechanical properties. This can be achieved through ring-opening polymerization of lactides. The lactide route is, however, relatively complicated, and alternative polymerization routes are of interest. In this paper we report the properties of a polymer made by a two-step process: first a condensation polymerization of lactic acid and then an increase of the molecular weight with diisocyanate. The end product is then a thermoplastic poly(ester-urethane). The hydroxylterminated prepolymer was made with condensation polymerization of L–lactic acid and a small amount of 1,4-butanediol. The polymerization was performed in the melt under nitrogen and reduced pressure. The preparation of poly(ester-urethane) was done in the melt using aliphatic diisocyanates as the chain extenders reacting with the end groups of the prepolymer. The polymer samples were carefully characterized, including preliminary degradation studies. The results indicate that this route to convert lactic acid into thermoplastic biodegradable polymer has high potential. Lactic acid is converted into a mechanically attractive polymer with high yield, which could make the polymer suitable for high volume applications. The mechanical properties of the poly(ester-urethane) are comparable with those of poly(lactides). Capillary rheometer measurements indicate that the polymer is processible both by injection molding and extrusion.     

E-Ring extended estrone derivatives: introduction of 2-phenylcyclopentenone to the estrone D-ring via an intermolecular Pauson-Khand reaction

An expedient synthetic route to E-ring extended estrone derivatives is reported. Estrone-derived cyclopentenones were accessed by an intermolecular Pauson-Khand (PK) cycloaddition. It was found that electron donating and withdrawing substituents in the arylalkyne increased and decreased the yields of PK products, respectively. The stereochemistry of the products was elucidated by X-ray and NMR studies.